Process for preparing 3-fluoroquinolines

A process for preparing 3-fluoroquinolines of formula (I):

• wherein R1, R2, R3 and R4, which may be identical or different, represent:
• a hydrogen atom;
• a fluorine atom;
• a linear, branched or cyclic alkyl radical optionally substituted with one to three fluorine atoms, with a group OR5 in which R5 represents a linear or branched alkyl radical, a hydrogen atom or a hydroxyl radical-protecting group, or with a group NR′R″ in which R′ and R″, which may identical or different, represent a linear or branched alkyl radical, a hydrogen atom or an amino radical-protecting group;
• a group OR6 in which R6 represents a hydrogen atom, a phenol-protecting group or a linear or branched alkyl radical optionally substituted with one to three fluorine atoms, with OR5 or with NR′R″ as defined above;
• a group NR′1R″1 in which R′1 and R″1 have the values of R′ and R″ or represent a linear or branched alkyl radical substituted with one to three fluorine atoms, with a group OR5 as defined above or with a group NR′R″ as defined above;
• a group CO2Ra, in which Ra represents a hydrogen atom, a linear or branched alkyl radical or a carboxyl radical-protecting group;
• a phenyl radical or a heteroaryl radical, optionally substituted with one or more of the substituents mentioned above, said process comprising:
• a) subjecting a compound of formula (IV):
• wherein R1, R2, R3 and R4 are as defined above, to a Hofmann degradation, so as to obtain a compound of general formula (III):
• wherein R1, R2, R3 and R4 are as defined above;
• b) treating said compound of formula (III) under conditions capable of forming the diazonium salt of general formula (II):
• wherein R1, R2, R3 and R4 are as defined above;
• and
• c) heating said compound of formula (II) in an inert organic solvent to form the compound of formula (I).